Thread cutting mechanism for sewing machines



Feb. 10, 1970 J. M- WASH- BURN THREAD CUTTING MECHANISM FOR SEWING MACHINES 2 Sheets-Sheet 1 Filed Sept. 1.7. 1968 FIG I INVENTOR JOHN M. WASHBURN.

ATTORNEYS.

Feb. 10, 1970 J. M. WASHBYURN I 3,494,315

THREAD CUTTING MECHANISM FOR SEWING MACHINES Filed Sept. 17. 1968 2 Sheets-Sheet 2 FIG. 2

JOHN M. WASHBURN,

BY -/ama, WW

ATTORNEYS.

United States Patent 3,494,315 THREAD CUTTING MECHANISM FOR SEWING MACHINES John M. Washburn, West Hartford, Conn., assignor to The Merrow Machine Company, Hartford, Conn., a

corporation of Connecticut Filed Sept. 17, 1968, Ser. No. 760,201 Int. Cl. Db 65/00 US. Cl. 112-252 6 Claims ABSTRACT OF THE DISCLOSURE A thread chain cutting mechanism for automatically cutting and removing thread chain from between successive articles sewn on a sewing machine. The cutter includes a pair of clipper blades mounted rearwardly of the needle plate and disposed transversely of the path of articles being sewn on the machine, with the cutting teeth on the blades being directed upwardly so that the sewn articles pass above the ends of the teeth. Thread chain formed between successive articles is drawn into the cutting teeth by a suction tube having an inlet positioned between the clipper blades and the needle plate of the machine, while guard means extending above the suction tube provides support for articles passing thereover.

This invention relates to thread cutting mechanisms, and more particularly to an improved thread cutting mechanism for use with a sewing machine to automatically remove the chain of stitches formed between successive articles sewn on the machine.

It has recently become quite common to employ an automatic trimming device, or thread cutter, on commercial sewing machines of the type commonly employed in the garment or hosiery industry to thereby eliminate the manual task of trimming articles sewn on the machines with scissors as was previously the custom. Numerous trimming devices have been developed and used, with more or less success, in recent years, with one such device being illustrated in Hornberger, Sr. Patent No. 3,109,399, assigned to the assignee of the present invention. The trimmer illustrated in this Hornberger patent employs a pair of reciprocating clipper blades, with sewn articles passing over the ends of the vertically disposed teeth on the blades, and a suction tube positioned behind the clipper blades to draw a chain of thread into the clipper teeth. The clipper illustrated in the Hornberger patent has not been satisfactory for commercial use in that it will not reliably cut the chain of thread joining successive articles, and there is a tendency for the reciprocating teeth of the clipper blades to impall and cut articles moving thereover. Accordingly, an object of the present invention is to provide an improved trimmer for a sewing machine which will reliably trim the thread chain from between successive articles sewn on the machine without damaging the articles.

Another object of the invention is to provide an improved trimmer employing clipper blades having upwardly directed cutting teeth with guard means to support an article passing between the machine needle plate and the cutting teeth while permitting the thread chain to be drawn beneath the guard by vacuum to be cut by the clipper teeth.

In the attainment of the foregoing and other objects, an important feature of the invention resides in providing a clipper mechanism having upwardly directed cutting teeth disposed beneath and transversely of the line of movement of articles passed through the sewing machine, with the clipper mechanism being spaced rearwardly of the machine needle plate. The upwardly directed open "ice inlet of a suction tube is positioned between the clipper mechanism and the needle plate, with the suction tube being positioned beneath the plane of the needle plate to draw thread chain downwardly to the underside of the articles which carry the thread chain intothe cutting teeth of the clipper. A guard structure is provided to support articles passing above the suction inlet while permitting thread chain to be drawn therethrough.

Other objects and advantages of the invention will become apparent from the following detailed description, taken with the drawings, in which:

FIG. 1 is an end elevation view of a sewing machine having a trimmer mechanism embodying the present invention mounted thereon;

FIG. 2 is a fragmentary top plan view of a portion of the sewing machine illustrated in FIG. 1;

FIG. 3 is a fragmentary view taken on line 3-3 of FIG. 2;

FIG. 4 is a fragmentary sectional view taken on line 4-4 of FIG. 3;

FIG. 5 is a fragmentary sectional view taken on line 5-5 of FIG. 3;

FIG. 6 is an exploded view of a trimmer mechanism employed in the invention; and

FIG. 7 is an exploded view of an alternate trimming mechanism.

Referring now to the drawings in detail, the trimmer mechanism of the present invention is illustrated as incorporated in the Well known Merrow overedge sewing machine, indicated generally by the reference numeral 10, which conventionally includes a work plate 12 pivotally supported, as by pin 14, to a work plate support block 16. The work plate 12 and the sewing machine needle plate 18 cooperate to define a substantially horizontal work support surface for articles (not shown) which are to be stitched by the machine as they are moved by the feed mechanism 20 beneath the machine presser foot 22 at the stitch forming station of the machine. While the work support plate extends alongside the needle plate and rearwardly therefrom to the back of the sewing machine, they do not provide support for an article in the area immediately behind the needle plate. The clipper mechanism described below is positioned in this area of no support, which may be referred to as an opening in the work support surface.

The thread chain cutting mechanism according to this invention includes a vertically disposed clipper assembly 24 positioned transversely of the path of movement of articles through the machine. The clipper assembly 24 includes a fixed forward blade 26 having a plurality of cutting teeth 28 formed on its upper edge, and a movable rear blade 30 having a plurality of cutting teeth 32 on its upper edge. Blade 26 is rigidly secured in fixed, spaced relation rearwardly of the needle plate 18 by a bolt 34 extending into work plate support block 16 with the top of the cutting teeth 28 positioned substantially in the plane on the top surface of needle plate 18. Integrally formed on and extending forward from each of the teeth 28 is an elongated guard bar, or finger 36, with the several guard bars 36 extending in parallel laterally spaced relation to one another to define a support for articles between the needle plate 20 and the cutting teeth 28, 32. Guard bars 36 each have their forward end 37 rounded to prevent sewn articles or thread chain from being snagged or caught thereon.

An elongated keyway 38 formed in the back surface of blade 26 receives and positions an integral key 40 formed on the forward surface of blade 30. Keyway 38 and key 40 provide a guide for blade 30 for reciprocal movement along the back surface of blade 26. Blade 30 is movably supported on blade 26 by a bolt 42 extending through an opening (not shown) in blade 26 and an elongated slot 44 in blade 30, with a Belleville spring Washer 46 and a lock nut 48 on bolt 42 resiliently urging the two blades into engagement with one another with sufficient force to provide the necessary cutting action upon reciprocation of blade 30. With blade 30 in position on blade 26, the upper end of the cutting teeth 32 are substantially coplaner with the upper end of teeth 28, thereby forming, in effect, a continuation of the work support surface. The cutting teeth of the clipper assembly preferably have broad, substantially fiat ends, and the teeth may be substantially uniform in cross sections throughout their lengths, While the teeth are indicated in the drawings as having substantially rectangular or isosceles trapezoidal cross sections, it is understood that they may be of any desired cross sectional shape to provide the desired cutting characteristics. However, in the embodiment in which the sewn articles pass directly over the ends of the cutting teeth, it is important that he cuting teeth do not have sharp points on their upper ends.

To move blade 30 reciprocably along keyway 38, a shaft 50 is rotatably mounted, as by journal 52, in an opening 54 in work plate support block 16. An arm 56 is rigidly mounted on the end of shaft 50 and projects radially therefrom with its radially outer end positioned within a slot 58 on the lower surface of blade 30. Arm 56 is caused to move in an arcuate path by oscillation of shaft 50 about its longitudinal axis by a crank arm 60 operatively connected, through a spherical bearing 62 to an eccentric drive (not shown) on the shaft 64 of an electric motor 66. Motor 66 is mounted on the sewing machine by a suitable bracket 68 and drives the shaft 59 in a manner quite similar to that illustrated in co-pending application Ser. No. 376,898 assigned to the assignee of the instant application.

To assure that the chain of stitches between successive articles is cut by the clipper mechanism, an elongated suction tube 70, connected to a suitable vacuum source (not shown) by a flexible hose 72, is positioned below the guard fingers 36 to draw the chain to the underside of the articles. Tube 70 terminates in an upwardly directed open inlet orifice 74 positioned below the guard members 36 and spaced beween the cutter blade 26 and the sewing machine needle plate 18.

In an alternate embodiment of the invention illustrated in FIG. 7, the cutting teeth 128 on the fixed clipper blade 126 are substantially identical to the cutting teeth 32 on movable blade 30. In this case, the guard fingers 136 are integrally formed on the back edge of the machine needle plate to provide support for an article as it passes above the open inlet 94 of vacuum tube 90 to the cutter mechanism 24.

mechanism 24. In this embodiment, the guard fingers 136 may either abut the vertical surface of the cutter teeth 126 or completely overlie the upper end of the cutting blades. When the guard fingers 136 overlie the cutting mechanism, the exact configuration of the cutting teeth is of no consequence since the sewn article would be protected even from sharp pointed teeth on the cutter blades. Further, it is contemplated that, if desired, the rear clipper blade could be reciprocated in this embodiment, and such an arrangement would merely require the rear blade to be mounted on the support 16 with the shaft 50 projecting therebeneath to reciprocate the forward blade.

While the embodiment illustrated in FIG. 7 shows the guard fingers 136 integrally formed on the needle plate, it is believed apparent that they could be formed independently, for example, as a part of a separate bracket, and mounted either on the machine frame or on the needle plate.

From the above it can be seen that articles fed through the machine by the feeding mechanism 20 will pass longitudinally over the elongated guardfingers 36 past the clipping mechanism 24. By applying sufficient vacuum to the suction tube 70 to induce a substantial flow of air into the open inlet nozzle 74, any chain of stitches or thread extending from the trailing edge of a stitched article toward the stitch forming station will be positively drawn down to the underside of the article and between the guard fingers and pulled into engagement with the cutting teeth of the clipper mechanism 24 by the normal passage of the articles toward the rear of the machine. Once the chain of stitches has been cut adjacent the trailing edge of an article, the chain will be drawn into the open inlet orifice 74 and extend in line from the stitching mechanism and held so that, when the leading edge of a subsequent article is fed through the machine the chain Will again be drawn into the cutting mechanism and clipped closely adjacent the forward edge of the article. The upwardly inclined cutting teeth provide a positive cutting action while the guard fingers provide support to prevent an article from being damaged by the cutting teeth. Further, use of the guard fingers permits use of a vacuum sufiicient to induce a substantial fiow of air into the tube to positively draw the chain of thread into the cutting mechanism, thereby minimizing the effort on the part of the sewing machine operator to guide the chain of thread over the cutting teeth.

While we have described and illustrated preferred embodiments of our invention, we wish it understood that we do not intend to be restricted solely thereto, but that we do intend to cover all embodiments thereof which would be apparent to one skilled in the art and which come within the spirit and scope of our invention.

What is claimed is:

1. In a sewing machine having a feeding mechanism for feeding articles over a substantially horizontal work support surface including the top surface of the sewing machine needle plate and past a stitch forming mechanism for forming a continuous chain of stitches in and between successive articles, and a thread cutting mechanism supported rearwardly of said needle plate in position to cut and remove the chain of stitches from between successive articles sewn on the machine, the improvement wherein said thread cutting mechanism comprises a clipper assembly including a pair of relatively movable clipper blades each having a plurality of cutting teeth formed thereon and supported in rearwardly spaced relation to said needle plate, said blades being disposed transverse to the path of movement of articles over said support surface and with said teeth projecting upwardly toward the plane of said support surface, a suction tube connected to a source of vacuum and having an upwardly directed open inlet positioned below said support surface between said clipper assembly and said needle plate, and guard means extending between said clipper assembly and said needle plate, said guard means forming a part of said support surface to support an article moving between said needle plate and said clipper assembly while permitting a chain of stitches between successive articles to be drawn below said support to be cut by said clipper assembly and removed by said suction tube.

2. In a sewing machine as defined in claim 1, the further improvement wherein said guard means comprises a plurality of elongated, laterally spaced fingers extending substantially parallel to the path of movement of an article through the machine.

3. In a sewing machine as defined in claim 2, the further improvement wherein said fingers are integrally formed with and project rearwardly from said needle plate.

4. In a sewing machine as defined in claim 2, the further improvement wherein said fingers are integrally formed with one of said clipper blades, said fingers constituting a laterally projecting extension of the cutting teeth on said one of said clipper blades.

5. In a sewing machine as defined in claim 1, the further improvement wherein said guard means overlays said clipper assembly to provide support for an article moving through said machine from said needle plate to a point past said clipper assembly.

6. In a sewing machine as defined in claim 1, the further improvement wherein said teeth on at least One of said clipper blades terminates in a flat, smooth surface extending substantially perpendicular to the longitudinal axis of the respective teeth, said substantially flat, smooth surface forming a part of said support surface to provide support for an article moving over said clipper assembly.

References Cited UNITED STATES PATENTS JAMES R. BOLER, Primary Examiner 

